1. Field of the Invention
The present invention relates to a vehicular air conditioner for controlling discharge temperature using a demand capacity change compressor.
2. Description of the Related Art
FIG. 4 shows a schematic construction of a conventional vehicular air conditioner. This vehicular air conditioner is an example of one installed in a standard automobile.
An air conditioning unit 10 for effecting cooling, heating or dehumidifying of introduced air and then discharging the air to a vehicle cabin comprises; an inside air/outside air box 10A, a blower unit 10B, a cooler unit 10C and a heater unit 10D. The air conditioning unit 10 is normally installed in a vehicle cabin under the dashboard. Moreover, numeral 11 denotes a control section for controlling various operations, and 12 denotes an operation section in which is arranged various switches which can be set up and operated according to the preference of a passenger, and an operation display section.
As follows is a brief description of the air conditioning unit 10 in air flow direction sequence.
Air introduced into the air conditioning unit 10 is selected from either outside air "a" outside of the vehicle cabin or inside air "b" inside of the vehicle cabin, by opening or closing an inside air/outside air changeover damper 13 in the inside air/outside air box 10A. Introduced outside air "a" or inside air "b" (hereinafter referred to as "introduced air") is drawn in by a blower fan 14 provided in the blower unit 10B, or as vehicle traveling wind, passed through an air conditioning duct AD and then sent to an evaporator 15 in the cooler unit 10C installed on the downstream side of the blower fan 14. To this evaporator 15 is supplied a low temperature and low pressure liquid refrigerant from a refrigerant system which forms a refrigerating cycle at the time of a cooling and dehumidifying operation, effecting cooling and dehumidifying by exchanging heat with the introduced air passing through the evaporator 15.
The refrigerant system is composed mainly of a compressor 16, a condenser 17, an expansion valve 18 and the evaporator 15, and a refrigerant circulating circuit is formed by connecting each unit with refrigerant piping 19.
The compressor 16 is connected via a compressor clutch 20 to an engine E as a drive source. The compressor 16 compresses a low temperature and low pressure gas refrigerant gasified by the evaporator 15, and supplies this to the condenser 17 as a high temperature and high pressure gas refrigerant.
The condenser 17 cools the high temperature and high pressure gas refrigerant supplied from the compressor 16 with outside air, such as traveling wind to condense and liquefy the gaseous refrigerant. The refrigerant liquefied in this way is separated into gas and liquid by a receiver (not shown), and then supplied to the expansion valve 18 as a high temperature and high pressure liquid refrigerant.
The expansion valve 18 decompresses and expands the high temperature and high pressure liquid refrigerant to give a low temperature and low pressure liquid (mist) refrigerant, and supplies the liquid refrigerant to the evaporator 15 installed in the air conditioning unit 10.
Hereafter, by circulating the refrigerant in the same manner, the refrigerating cycle is formed.
On the downstream side of the evaporator 15, a heater unit 10D is provided in a prescribed location, and a heater core 21 is installed therein. To this heater core 21 is introduced a high temperature engine coolant for which the flow rate is controlled by a water valve 22, effecting heating by exchanging heat with the passing introduced air. Moreover, the flow rate of the introduced air passing through the heater core 21 can be adjusted by the opening of an air mix damper 22.
As a result, introduced air can be adjusted to a predetermined temperature in the heater unit 10D, or air-conditioned air can be blown selectively by the damper operation from a defroster air outlet 23, a face air outlet 24 and a foot air outlet 25 provided in the heater unit 10D.
Such an air conditioning unit 10 is so constructed that the heater core 21 for effecting heating is arranged on the downstream side of the evaporator 15 which effects cooling and dehumidifying, enabling dehumidifying air conditioning where cooled and dehumidified introduced air is heated again to a suitable temperature. There is thus the merit that the temperature can be maintained and condensation on the window can be cleared.
Particularly, in an electric car or a hybrid car (using both an electric motor and an internal combustion engine as a drive source), a heat pump type air conditioner is adopted, since there is the case where no engine coolant is obtained as a heat source for heating, or the engine coolant is insufficient. In this case, a four way valve is arranged in the refrigerating cycle to reverse the refrigerant flow direction for the heating operation and for the cooling operation. Consequently, at the time of the heating operation, the above described evaporator 15 operates as a condenser, and the condenser 17 operates as an evaporator. As a result, the vehicle cabin can be heated with heat drawn from the outside air.
With the above described conventional vehicular air conditioner, since the compressor 16 is driven using the engine E as a drive source, the capacity thereof varies largely depending upon the traveling condition of the vehicle. That is to say, the discharge pressure HP and the suction pressure LP vary depending upon fluctuations in engine RPM. Consequently, since the cooling capacity of the refrigerating cycle increases substantially linearly in proportion to the RPM of the engine E, then in many cases, the cooling capacity does not meet the demand on the air conditioner side.
Therefore, with a conventional vehicular air conditioner, the cooling capacity is adjusted by switching the compressor clutch 20 ON/OFF, or cool air and warm air are mixed by making high temperature engine coolant flow into the heater core 21 to obtain a mild discharge temperature.
There is thus a problem in that a shock caused at the time of switching the clutch ON/OFF impairs the traveling feeling, or that variations in the discharge temperature impairs the air conditioning feeling. Moreover, there is another problem in that the method of mixing cool air and warm air to adjust the discharge temperature causes a needless energy loss, which goes against the recent trend of energy saving.